The present invention relates to a dense phase powder pump for conveying coating powder.
Accordingly, the invention relates in particular to a dense phase powder pump for conveying coating powder from a first powder reservoir to a second powder reservoir arranged downstream of the dense phase powder pump or a powder spray-coating gun or similar device for spraying coating powder disposed downstream of the dense phase powder pump.
The invention further relates to a method of conveying coating powder from a first powder reservoir to a second powder reservoir disposed downstream of the first powder reservoir or a powder spray-coating gun or similar device for spraying coating powder disposed downstream of the first powder reservoir.
Dense phase powder pumps of the above type are generally known from the prior art.
For example, published document EP 1 551 558 A1 relates to a dense phase powder pump having a first powder conveyor chamber and a second powder conveyor chamber arranged parallel to the first powder conveyor chamber. The two powder conveyor chambers of this known prior art dense phase powder pump are limited both on the intake side as well as the discharge side by a mechanically actuated pinch valve arrangement.
It is specifically provided for the powder tube connected to the respective powder conveyor chambers of the dense phase powder pump to be deformable in the intake or respectively discharge region of the dense phase powder pump by means of a mechanical punch in order to squeeze or open the tube section as needed. A filter tube is allocated to each powder conveyor chamber of this known prior art dense phase powder pump which limits the circumference of the respective powder conveyor chamber. The filter tube is permeable to air but not to coating powder and is surrounded by an annular chamber to which negative pressure or compressed air can be alternatingly connected. Coating powder can thus be alternatingly suctioned into each powder conveyor chamber or expelled from the respective powder conveyor chamber by compressed air. The two parallel arranged powder conveyor chambers are actuated in phase opposition, which means that one of the two powder conveyor chambers draws in coating powder through the powder inlet of the dense phase powder pump while the other of the two powder conveyor chambers expels a portion of coating powder previously suctioned into the powder conveyor chamber via the powder outlet of the dense phase powder pump.
Dense phase powder pumps having a plurality, particularly two powder conveyor chambers connected in parallel are known from the WO 2005/005060 A2 (US 2006/0193704 A1) published document, the DE 199 59 473 A1 (US 2001/0003568 A1) published document and the EP 1 752 399 A1 published document.
The use of dense phase powder pumps to convey coating powder to respective devices for spraying coating powder, such as powder spray-coating guns in particular, is known from the DE 196 11 533 B4, WO 2004/087331 A1 and EP 1 566 352 A2 published documents.
Before the use of dense phase powder pumps of the above type to convey coating powder became known, powder pumps configured as injectors were used and these are still being used today in the conveyance of coating powder. However, unlike the dense phase powder pumps of the type cited above, powder pumps configured as injectors have the disadvantage of usually only being able to convey a small amount of coating powder per unit of time.
Dense phase powder pumps of the type cited at the outset have inasmuch become established in practice, particularly for applications in which a relatively large volume of coating powder is to be conveyed per unit of time.
Practical use has, however, shown that the operation of a dense phase powder pump such as known for example from the EP 1 551 558 A1 published document has multiple disadvantages particularly in terms of its maintenance and the resulting operational costs. This is due to the fact that—in contrast to powder pumps configured as injectors—a dense phase powder pump of the type described above has a relatively high number of components subject to continuous operation when the dense phase powder pump is in operation. For example, a conventional dense phase powder pumps makes use of at least four alternatingly actuated valves, whereby servicing a single valve inevitably entails the loss of the dense phase powder pump for a given maintenance period.
Because conventional dense phase powder pumps use at least two powder inlet valves on the intake side and at least two powder outlet valves on the discharge side, this accordingly inevitably reduces the span of time over which the dense phase powder pump can be operated without being serviced.
Moreover, conventional dense phase powder pumps require relatively complex operational diagrams in order to be able to coordinate the control of the pump's individual components subject to being alternatingly actuated.
Based on this problem, the present invention addresses the task of further developing a dense phase powder pump of the type cited at the outset to the effect of it needing fewer high-maintenance components, whereby at the same time the powder conveying capability of the pump remains as unchanged as possible.
It is furthermore a task of the invention to provide a simpler structural design of a dense phase powder pump as cited at the outset, in particular simplify it or reduce its size.
A correspondingly simplified method for conveying coating powder is moreover to be specified.